Optical band gap of the filled tetrahedral semiconductor LiZnAs

We report on the optical band gap of the filled tetrahedral semiconductor LiZnAs [viewed as a hypothetical zinc-blende (ZnAs${)}^{\mathrm{-}}$ lattice partially filled with He-like ${\mathrm{Li}}^{+}$ interstitials]. The band-structure nature of LiZnAs is found to be direct with a forbidden gap of 1.51 eV at 300 K. The fundamental absorption edge is shifted to the higher energy by 100 meV at 77 K. In the photoluminescence study at 12 K an emission associated with a donor-acceptor pair is observed at around 814 nm (1.52 eV), indicating that the estimated band gap is a reasonable value, but the band-edge emission is not found. We suggested that the larger band gap of LiZnAs, as compared to that of GaAs is attributed to the higher ionicity.